However, these surveys are problematic because they tend to look at household income and tally only a mother's children, she says. The children of divorced and remarried men tend to get left out.
To correct for this bias, Nettle and Newcastle colleague Thomas Pollet looked at previously gathered data on more than 11,000 British men and women, all born between 3 and 9 March 1958, called the National Child Development Study.
The study has tracked income, marriage and fertility of study participants since birth. "It's a great resource," Nettle says.
Now that study participants have entered their late 40s – the study used data from 2004 – nearly all participants have stopped having children.
With carefully collected figures on male and female income and fertility, Nettle and Pollet found that, for men, the more money they make, the more kids they sire on average. Men who earn £10,000 a year fathered one child on average, while fathers who pulled in £50,000-plus sired more than two kids.
But rich men didn't have larger families, rather they are more likely to find mates, Nettle says.
So despite the industrial revolution, gender equity, and birth control, rich and powerful men are more likely to pass on their genes than poorer and less powerful men.
"A deep aspect of the way human society works is that men with a lot of resources use their resources to achieve high reproductive success," says Nettle. "In a way, what we're saying in this paper is that a modern industrial society like Britain isn't so different."
The difference between modern Britain and medieval Europe or contemporary African hunter-gatherers is a matter of degree, not kind, he argues.
Human selection for male wealth even compares with sexual selection in animals for male traits favoured by females, Nettle and Pollet found. Based on a quantitative database of animal traits known to affect female choice, male wealth fell square in the middle.
The power of sexual selection for wealth in males compares to bill size in the large cactus finch, one of Darwin's Galapagos finches, Nettle says.
But while a peacock's tail or a bull's horns have an obvious basis in biology, male wealth is harder to pin to genetics, Nettle says. Ambition, intelligence and financial savvy probably have some heritable aspects, but social status, inheritance and upbringing are just as likely to affect a son's future income, he says. "We get so much from our parents, as humans, besides genetics."
Journal reference: The American Naturalist (November 2008)
Fuel thinner turns diesel cars into greener machines
* 16:41 29 September 2008
* NewScientist.com news service
* Phil McKenna
A small gadget that can be fitted to diesel engines boosts fuel efficiency by up to 19% and can make them run more cleanly, engineers report. A weak electric field is used to make fuel less viscous before it is injected into the engine. That makes it possible to spray smaller drops that burn more completely.
The device was developed at Temple University in Philadelphia, Pennsylvania and costs less than $200 to produce. In tests over six months on a 2002 Mercedes-Benz 300D sedan, a prototype device increased fuel efficiency by 12 to 15% under urban driving conditions, and 19% in highway driving – taking it from 32 to 38 miles per gallon.
"This is the biggest efficiency increase since the advent of fuel injection," claims Rongjia Tao from Temple University. The device has been licensed to Californian firm Save the World Air, which is now testing it in road haulage vehicles.
An electric field makes diesel thinner because some molecules in the fuel become charged and aggregate together, reducing their overall surface area. That means less friction between them, and a less viscous fuel.
Tao and colleagues believe fuel efficiency gains were lower under stop-start urban driving conditions because the rate at which fuel flows through their device constantly varies.
They are working on a version that varies its electric field to match fuel flow rate and keep viscosity constantly reduced.
Matt Thomas of CFD Research Corporation works on similar fuel electrification techniques. He says fitting the device to new cars will not produce such spectacular efficiency gains, but adds that it would still cut emissions. "[If] you charge spray prior to fuel injection you could lower particulate emissions by as much as a factor of 10." Journal reference: Energy and Fuels (DOI: 10.1021/ef8004898)
Private rocket achieves orbit on fourth try
* 18:10 29 September 2008
* NewScientist.com news service
* Rachel Courtland
After three failed attempts, the private space firm SpaceX successfully launched a rocket into orbit on Sunday, marking what may be the beginning of a significant drop in the cost of spaceflight.
The two-stage Falcon 1 rocket launched at 1115 GMT from Omelek Island on the Kwajalein Atoll in the Pacific Ocean, roughly 4000 kilometres southwest of Hawaii.
Paypal entrepreneur Elon Musk has said he founded SpaceX with the aim of driving down the cost of space access. The firm estimates that Falcon 1 flights will cost as little as $7.9 million a piece, roughly three times less expensive than current launches. In an interview with New Scientist on Friday, Musk said if the launch was successful, "I won't need a rocket, because I'll be over the Moon."
The rocket's second stage achieved a stable orbit more than 500 km above Earth. The first stage, which the firm aims to make recoverable, is thought to have burned up when it re-entered the atmosphere.
Sunday's success is the firm's fourth attempt to reach orbit, but only the second test of its new, fuel-cooled Merlin 1C engine.
The firm lost the first such engine during a launch attempt on 3 August. The engine's first stage still had considerable thrust after it was shut down, which caused it to ram into the rocket's second stage after the two had separated.